Well, I dont think you were advised correctly by NR - but its probably too late to change that now. As far as I know, you should have a set time to cancel any insurance or loan in the cooling off period (is it 14 days)? I did successfully cancel PPI on one of my agreements within the cooling off period a few years ago.
If for any reason your IVA fails, then you could go for the jugular and attempt to get the PPI charges refunded if you think it wasnt above board. I think this could involve putting the debt into dispute, which would also mean they cant chase you for the money until the matter is resolved - buying you a bit of extra time as well. You probably want to visit the consumer action group
www.consumeractiongroup.com website for info on claiming back PPI and charges etc.
I doubt you would ever get to speak to a person who judges a IVA proposal - so probably little point speaking to NR personally about what they might accept. I would leave that to your IP, as they will be in contact with the people that matter.